none The parasitic wasps Leptopilina heterotoma (Thomson) and Asobara tabida (Nees) usually refrain from laying eggs in hosts that have already been parasitized by themselves or by a conspecific (=intraspecific host discrimination). In contrast to intraspecific host discrimination, interspecific host discrimination, in which females refrain from laying eggs in hosts that have already been parasitized by the other species, is not found in these sympatric parasitoid species. Because the authors expected that development of interspecific host discrimination would increase the fitness of the wasps, they wondered why this strategy had not evolved in L. heterotoma and A. tabida . They therefore developed a simulation model of the parasitization process, in which interspecific host discrimination can be included. The results imply that, assuming that female wasps carry an ample supply of eggs, the development of interspecific host discrimination by L. heterotoma or A. tabida will not lead to increased fitness, even under extreme circumstances. Hence, interspecific host discrimination will not evolve.